A man rows 18 km downstream in 4 hours and returns upstream in 12 hours. Calculate the speed of the stream in km/hr.

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Accepted Answer

To solve this problem, we first calculate the downstream and upstream speeds using the formula $$ 	ext{Speed} = \frac{	ext{Distance}}{	ext{Time}} $$.

**Step 1: Calculate Downstream Speed**  
The man rows 18 km downstream in 4 hours:  
$$
	ext{Downstream Speed} = \frac{	ext{Distance}}{	ext{Time}} = \frac{18}{4} = 4.5 \, 	ext{km/hr}.
$$

**Step 2: Calculate Upstream Speed**  
The man rows the same distance upstream (18 km) in 12 hours:  
$$
	ext{Upstream Speed} = \frac{	ext{Distance}}{	ext{Time}} = \frac{18}{12} = 1.5 \, 	ext{km/hr}.
$$

**Step 3: Calculate Speed of the Stream**  
The speed of the stream can be found using the formula:  
$$
	ext{Speed of Stream} = \frac{	ext{Downstream Speed} - 	ext{Upstream Speed}}{2}.
$$

Substituting the values:  
$$
	ext{Speed of Stream} = \frac{4.5 - 1.5}{2} = \frac{3}{2} = 1.5 \, 	ext{km/hr}.
$$

Thus, the speed of the stream is **1.5 km/hr**.

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